Question

我正在尝试使用count来解决这个问题。它为作者返回了正确数量的书籍，但根据问题，我不能两次拥有相同的书名。是否有更好的运算符用于此问题？

以下是问题：

查找图书馆拥有最多不同图书的作者姓名（同一本图书的多个副本只计为一本图书）

这是我的代码：

CREATE TABLE Book
(
    bookID INT,
    ISBN INT,
    title varchar (30),
    author  varchar (20),
    publish_year INT,
    category varchar(20),
    PRIMARY KEY (bookID)
);  

CREATE TABLE Member
(
    memberID INT,
    lastname varchar (20),
    firstname varchar (20),
    address varchar(20),
    phone_number INT,   
    limit_ INT,
    PRIMARY KEY (memberID)
);

CREATE TABLE CurrentLoan
(
    memberID INT ,
    bookID INT,
    loan_date DATE,
    due_date DATE,
    PRIMARY KEY (memberID, bookID),
    FOREIGN KEY (memberID) REFERENCES Member(memberID),
    FOREIGN KEY (bookID) REFERENCES Book(bookID)
);

CREATE TABLE History
(
    memberID INT,
    bookID INT,
    loan_date DATE,
    return_date DATE,
    PRIMARY KEY (memberID, bookID, loan_date),
    FOREIGN KEY (memberID) REFERENCES Member(memberID),
    FOREIGN KEY (bookID) REFERENCES Book(bookID)
);

INSERT INTO Book 
VALUES (10, 1113312336, 'The Dog', 'Jack Crow', 1990, 'fiction');
INSERT INTO Book 
VALUES (12, 2221254896, 'Worms', 'Jim Kan', 2013, 'childrens');
INSERT INTO Book 
VALUES (13, 3332546987, 'Crow', 'Jan Flo', 2000, 'fiction'); 
INSERT INTO Book 
VALUES (14, 4443456215, 'Big Dog', 'Lan Big', 1993, 'children');
INSERT INTO Book 
VALUES (15, 5552314569, 'Green Apple', 'Theo Brown', 1978, 'children');
INSERT INTO Book 
VALUES (16, 6664581631, 'Red Bean', 'Khang Nk', 2017, 'fiction');
INSERT INTO Book 
VALUES (17, 7771452369, 'XML and XQuery', 'Author Le', 2017, 'non-fiction');
INSERT INTO Book 
VALUES (18, 8881245525, 'The Dark Room', 'Jack Se', 2017, 'fiction');
INSERT INTO Book 
VALUES (19, 9991123546, 'Yellow Bird', 'Jake Red', 2014, 'refrence');
INSERT INTO Book 
VALUES (20, 1122112356, 'XQuery: The XML Query Language', 'Heart Le', 2002, 'fiction');
INSERT INTO Book
VALUES (21, 1212121212, 'Gone Fishing', 'Shel Silverstein', 1964, 'reference');
INSERT INTO Book
VALUES (22, 2121212121, 'Gone Fishing', 'Shel Silverstein', 1964, 'reference');
INSERT INTO Book
VALUES (23, 1313131313, 'The Lazy Dog', 'Jake Red', 2016, 'children');
INSERT INTO Book
VALUES (24, 3131313131, 'The Red Bird', 'Jake Red', 2016, 'children');
INSERT INTO Book
VALUES (25, 1414141414, 'The Very Blue Boy', 'Ben Jen', 2006, 'fiction');

INSERT INTO Member 
VALUES (001, 'Lee', 'Nancy', 'Brownlea Drive', 1254896325, 10);
INSERT INTO Member 
VALUES (002, 'Le', 'Ray', '10th Street', 1234561256, 2);
INSERT INTO Member 
VALUES (003, 'Kan', 'Charlie', '5th Street', 1234567236, 8);
INSERT INTO Member 
VALUES (004, 'Brown', 'Joe', 'Elm Street', 1234567845, 9);
INSERT INTO Member 
VALUES (005, 'Smith', 'John', '33 East', 1234567890, 3);
INSERT INTO Member 
VALUES (006, 'Kope', 'NON', '358 Seng', 2145345625, 5);
INSERT INTO Member 
VALUES (007, 'Jones', 'David', '4th Street', 14812365789, 10);

INSERT INTO CurrentLoan VALUES (002, 20, '13-SEP-17', '14-NOV-17');
INSERT INTO CurrentLoan VALUES (001, 19, '13-JAN-17', '15-NOV-17');
INSERT INTO CurrentLoan VALUES (006, 17, '14-FEB-17', '12-MAR-17');
INSERT INTO CurrentLoan VALUES (003, 15, '12-OCT-17', '09-NOV-17');
INSERT INTO CurrentLoan VALUES (005, 18, '13-APR-17', '12-MAY-17');
INSERT INTO CurrentLoan VALUES (007, 25, '02-OCT-17', '25-DEC-17');

INSERT INTO History VALUES (002, 17, '14-Jan-17', '04-JUN-17');
INSERT INTO History VALUES (003, 19, '12-Jan-17', '04-NOV-17');
INSERT INTO History VALUES (001, 13, '14-APR-17', '08-OCT-17');
INSERT INTO History VALUES (006, 20, '14-MAY-17', '04-DEC-17');
INSERT INTO History VALUES (007, 12, '02-OCT-16', '25-DEC-16');
COMMIT;

这是我的问题：

SELECT 
    author, COUNT(*) AS numberofbooks
FROM 
    Book
GROUP BY 
    author 
ORDER BY 
    numberofbooks DESC;

Answer 1

就您的查询而言，它是正确的，请检查作者姓名或拼写差异可能有额外的空间。

Answer 2

要消除重复的标题，您需要在子查询中生成唯一的行，然后计算这些行，如下所示：

SELECT Author, Count(*) NumberOfTitles
FROM
(
    SELECT DISTINCT Author, Title
    FROM   Book
) Subquery
GROUP BY Author

Answer 3

我只需在|¯¯¯¯¯¯¯|Arlidio|_______|之前使用distinct。

title

我正在尝试在此查询中使用count

3 个答案: